Metering valves are a common means by which aerosols are dispensed from aerosol containers. Metering valves are particularly useful for administering medicinal formulations that include a liquefied gas propellant and are delivered to a patient in an aerosol.
When administering medicinal formulations, a dose of formulation sufficient to produce the desired physiological response is delivered to the patient. The proper, predetermined amount of the formulation must be dispensed to the patient in each successive dose. Thus, any dispensing system must be able to dispense doses of the medicinal formulation accurately and reliably to help assure the safety and efficacy of the treatment.
Metering valves have been developed to provide control over the dispensing of medicinal aerosol formulations. A metering valve may be used to regulate the volume of a medicinal formulation passing from a container to a metering chamber, which defines the maximum amount of the formulation that will be dispensed as the next dose. The precise dosage metered by the metering chamber may be dependent, in part, upon the physical conditions under which the medicinal formulation is permitted to fill the metering chamber. Reliable and controllable flow of the medicinal formulation into the metering chamber may contribute to the accuracy and/or precision of the metering of successive doses of the formulation. Thus, reliable and controllable flow of the medicinal formulation into the metering chamber may improve performance of the metering valve and, therefore, may be highly desirable.
In some metering valves, the metering chamber fills with the medicinal formulation prior to the patient actuating the valve stem and thereby releasing the dose. The metering chamber is refilled with formulation after dispensing one dose so that the metering valve is ready to discharge the next dose. Consequently, the metering chamber contains formulation at all times except for the brief time during which the valve stem is depressed by the user to discharge a dose. Also, the passageways through which the formulation must flow to reach the metering chamber are often narrow and tortuous. As a result, metering valves configured in this way have a number of disadvantages resulting in, for example, erratic dosing due to loss of prime, i.e., the occurrence of vapor or air voids in the metered volume, which may leading to a shortfall in the volume of dose being metered by the valve.
In other metering valves, the metering chamber does not materialize unless and until the valve stem is actuated. Actuation of these valve stems can be divided into a filling stage and a discharge stage. The filling stage begins as the valve stem is depressed during actuation. The action of depressing the valve stem causes the formation of a transient metering chamber. As the valve stem is depressed, the transient metering chamber expands and formulation enters the metering chamber. As displacement of the valve stem continues, a stage is reached at which filling of the transient metering chamber stops. Eventually, displacement of the valve stem continues to the discharge stage, in which the metered formulation is discharged. In these valves, a single actuation thus causes rapid filling of the transient metering chamber followed by discharge of the formulation to the patient. Thus, the metered formulation does not reside for any appreciable amount of time in the metering chamber.
While a metering valve having a transient metering chamber provides advantages over other types of metering valves for the delivery of aerosol formulations, the flow of formulation from the container to the metering chamber may be disrupted. When this happens, formulation may be delivered in inconsistent or inaccurate doses.
What is needed is a valve stem for a metered dose inhaler that improves flow of formulation into the metering chamber, thereby providing consistent, accurate, dosages of formulation, even when actuated rapidly.
It has been determined that one cause of disrupted flow of formulation may be due to the design of the valve stem in the metering valve. A seal typically isolates the metering chamber from the aerosol container once the correct volume of formulation has been metered. To accomplish this, the seal must occlude the flow path, through which formulation must pass in order to fill the metering chamber, as the valve stem is depressed beyond the filling stage. As used herein, occlude refers to at least a partial closing off of an opening by a seal, gasket, or diaphragm. In certain metering valves, the passageways leading from the container to the metering chamber can begin to become occluded well before the formulation has completed filling the metering chamber. This effectively begins to cut off flow of formulation into the metering chamber while the valve stem is still in the filling stage of actuation.
Also, the design of the valve stem may cause regions of recirculation or localized low pressure to develop in the flow of formulation into the metering chamber. Such low pressure regions can lead to incomplete metering of the formulation by allowing bubbles to form in the metered volume, particularly when the patient actuates the valve rapidly or rapid actuation occurs due to the mechanism of a breath actuated device.
The present invention provides a valve stem for a metered dose inhaler that improves the flow of formulation into the metering chamber. The novel stem design has a short, but circumferentially widened channel opening that, in many embodiments, enhances the flow of formulation into the metering chamber. Accordingly, the present invention provides an aerosol valve stem including a body that includes a body wall defining an internal chamber; at least one inlet port through the body wall in fluid communication with the internal chamber; a channel opening in the body wall having a height and a width wherein the width is greater than the height; and at least one channel providing fluid communication between the internal chamber and the channel opening.
In some embodiments, the valve stem may include a plurality of channel openings in the body wall. In these embodiments, the plurality of channel openings may define a cumulative width that is greater than the height of the channel openings.
In another aspect, the present invention provides a method of delivering an aerosol dose of medicine including providing an inhaler that includes an aerosol valve stem including: a body that includes a body wall defining an internal chamber, at least one inlet port through the body wall in fluid communication with the internal chamber, a channel opening in the body wall having a height and a width wherein the width is greater than the height, at least one channel providing fluid communication between the internal chamber and the channel opening; providing a formulation of aerosol medicine contained within the inhaler; and actuating the inhaler.
In yet another aspect the present invention provides a metering valve that includes a housing that includes an internal chamber defined by one or more chamber walls, the internal chamber comprising an outlet aperture; a diaphragm positioned at the outlet aperture and in sealing engagement with at least a portion of the housing; a metering gasket in sealing engagement with one or more chamber walls; a valve stem including: i) a body that comprises a body wall defining an internal chamber, ii) at least one inlet port through the body wall in fluid communication with the internal chamber, iii) a channel opening in the body wall having a height and a width wherein the width is greater than the height, and iv) at least one channel providing fluid communication between the internal chamber and the channel opening, wherein the valve stem passes through the aperture in slidable sealing engagement with both of the diaphragm and the metering gasket; and an annular space having a width defined by a distance between the chamber wall and the valve stem.
In some embodiments, the valve stem may include a plurality of channel openings in the body wall. In these embodiments, the plurality of channel openings may define a cumulative width that is greater than the height of the channel openings. In certain embodiments, the height of at least one channel opening may be from about 1 to about 5 times the width of the annular space.